Inkjet printers operate a plurality of inkjets in each printhead to eject liquid ink onto an image receiving member. The ink can be stored in reservoirs that are located within cartridges installed in the printer. Such ink can be aqueous ink or an ink emulsion. Other inkjet printers receive ink in a solid form and then melt the solid ink to generate liquid ink for ejection onto the imaging member. In these solid ink printers, the solid ink can be in the form of pellets, ink sticks, granules, pastilles, or other shapes. The solid ink pellets or ink sticks are typically placed in an ink loader and delivered through a feed chute or channel to a melting device, which melts the solid ink. The melted ink is then collected in a reservoir and supplied to one or more printheads through a conduit or the like. Other inkjet printers use gel ink. Gel ink is provided in gelatinous form, which is heated to a predetermined temperature to alter the viscosity of the ink so the ink is suitable for ejection by a printhead. Once the melted solid ink or the gel ink is ejected onto the image receiving member, the ink returns to a solid, but malleable form, in the case of melted solid ink, and to gelatinous state, in the case of gel ink.
A typical inkjet printer uses one or more printheads with each printhead containing an array of individual nozzles through which drops of ink are ejected by inkjets across an open gap to an image receiving surface to form an ink image during printing. The image receiving surface can be the surface of a continuous web of recording media, a series of media sheets, or the image receiving surface can be a rotating surface, such as the surface of a rotating print drum or endless belt. Images printed on a rotating surface are later transferred to recording media by mechanical force in a transfix nip formed by the rotating surface and a transfix roller. In an inkjet printhead, individual piezoelectric, thermal, or acoustic actuators generate mechanical forces that expel ink through an aperture, usually called a nozzle, in a faceplate of the printhead. The actuators expel an ink drop in response to an electrical signal, sometimes called a firing signal. The magnitude, or voltage level, of the firing signals affects the amount of ink ejected in an ink drop. The firing signal is generated by a printhead controller with reference to image data. A print engine in an inkjet printer processes the image data to identify the inkjets in the printheads of the printer that must be operated to eject a pattern of ink drops at particular locations on the image receiving surface to form an ink image corresponding to the image data. The locations where the ink drops landed are sometimes called “ink drop locations,” “ink drop positions,” or “pixels.” Thus, a printing operation can be viewed as the placement of ink drops on an image receiving surface with reference to electronic image data.
In order for the printed images to correspond closely to the image data, both in terms of fidelity to the image objects and the colors represented by the image data, the printheads are registered with reference to the image receiving surface and with the other printheads in the printer. Registration of printheads refers to a process in which the printheads are operated to eject ink in a known pattern and then the printed image of the ejected ink is analyzed to determine the relative positions of the printheads with reference to the imaging surface and with reference to the other printheads in the printer. Operating the printheads in a printer to eject ink in correspondence with image data presumes that the printheads are level with one another across a width of the image receiving member and that all of the inkjets in the printhead are operational.
Two or more printheads can be mounted linearly, or in other configurations, to a support structure, to form an array of printheads. Not only is registration between individual printheads important, but control of the registration of the supporting structure with respect to the image receiving surface is also desirable. The gap, or distance between support structure and the imaging surface, is controlled to optimize the imaging process. If the gap is too small, burnishing of the printheads can occur when the image receiving surface contacts the face of the printheads. Burnishing not only can reduce the life of the printheads, but can produce poor image quality and increased downtime of the printer during maintenance. If the gap it too large, image quality can suffer, particularly in high speed printers, where a large gap can result in the ink drops being deposited at unintended locations.
The setting of a proper gap is important where a printer is designed to accept a variety of imaging surfaces, including surfaces having a tendency to wrinkle, having different thicknesses, or having uneven surfaces. A thin layer of polytetrafluoroethylene (PTFE) is disposed on the printheads to provide accurate imaging. The PTFE layer controls the drooling pressure at the orifices of the printhead and should not be touched or burnished by wax or paper. If the PTFE is damaged, the drooling pressure can drop which in turn can alter the path of ejected ink drops as well as drooling, or dripping of ink during printing resulting from weak and missing inkjets.
Continuous web media is transported from a paper manufacturer to an end user as a roll of material. The outer edges of the web roll can be adversely affected during transportation due to shipping and handling. For instance either of the edges, which are often exposed, can be adversely affected. When the damaged edges move through the printer, the damaged edge can strike the face of the printhead due to the small gap between the surface of the print media and face of the printhead. These damaged edges can adversely impact the printheads. To reduce the risk of contact with the printheads, an operator typically cuts off about one inch of the outer edge of the web roll before mounting the web roll to the machine. While removing the outer one inch of material from the edges of the web roll can eliminate or substantially reduce damage to the printheads, this procedure is not desirable since both material and time are wasted.